In the manufacture of glass panes for use in windows, it is common to lay down a deposit, usually by sputtering techniques, of a thin film of a metal such as silver or copper to change the reflectance and absorbance characteristics of the glass pane. Reference is made to U.S. Pat. No. 4,462,884 (Gillery, et al.) with respect to the production of silver/copper films by cathode sputtering, and to U.S. Pat. No. 4,166,018 (Chapin) with respect to the method of coating a substrate utilizing a cathode sputtering technique involving a magnetic field to improve the sputtering efficiency.
Thin, transparent films of silver, copper and the like are susceptible to corrosion (e.g., staining) when they are brought into contact, under moist or wet conditions, with various staining agents such as atmosphere carried chlorides, sulfides, sulfur dioxide and the like. Films of this type commonly are employed on inner surfaces of multi pane glass units so that the films are maintained in a dry condition by desiccants or the like that remove moisture from the interpane spaces. Staining can occur, however, when coated panes of glass are stored for later fabrication into insulating glass units. To avoid staining during storage, sheets of treated paper have been employed between coated glass panes to prevent moisture and staining agents such as those described above from coming into contact with the coated metal films. Treated paper interliners of this type commonly are used but once. The paper interliner cost, plus the additional labor required to insert and remove the paper liners, adds significantly to the cost of the coating and fabricating process.
To avoid the use of a treated paper interliner, it has been proposed to add to the coated panes, as an outer layer, a thick coating (100-120 Angstroms) of titanium dioxide, deposited by sputtering from a titanium metal target in the presence of oxygen. Titanium dioxide layers of at least this thickness have been found to serve as barriers, restraining corrosive or staining agents such as those described above from penetrating through them and coming into contact with the one or more metal layers therebeneath. The deposition of such thick coatings of titanium dioxide, however, has given rise to other problems. Titanium dioxide can be sputtered, as above described, only very slowly. That is, the rate of deposition is quite low. This, in turn, greatly reduces the speed at which glass panes can be provided with a series of coatings in a single coating apparatus, and consumes large quantities of electric power.